The present invention relates to a polyorganosiloxane composition containing a storage stabilizer having a specific chemical structure. More particularly, it relates to a polyorganosiloxane composition which exhibits excellent storage stability at room temperature and can be quickly crosslinked or cured through addition reaction by heating.
There have been proposed various addition-curable compositions (or compositions capable of being cured through addition reaction) which contain mainly of an alkenyl group-containing polyorganosiloxane, a polyorganohydrogensiloxane and a platinum catalyst and incorporated with an additive for providing storage stability to the composition at room temperature. It is required that such compositions can be stored stably for a long period of time at room temperature, even after all the components have been mixed, and that such compositions can be cured only heating.
Known storage stabilizers for addition curable compositions include benzotriazoles, such as those described in Japanese Patent Publication No. 25,069/65; acetylene group-containing alcohols, such as those described in U.S. Pat. No. 3,445,420; and acrylonitriles, such as those described in Japanese Patent Publication No. 22,018/60. However, these known storage stabilizers are unsatisfactory in their stabilizing effects. Even when the known stabilizers are used, the viscosity of such compositions gradually increases or the compositions turn into gel when stored for an extended period of time at room temperature. When the stabilizers are used in large quantities in order to suppress the increase in viscosity for longer than periods, there is required higher temperatures and longer periods of time for curing. Further, there is an increased problem with phase separation during storage at room temperature because of poor compatibility between the stabilizers and the polysiloxanes. Still further, when such compositions are incorporated with an acetylene group-containing alcohol or acrylonitrile in a large quantity and cured with hot air of ca. 150.degree. C., the curing of the compositions proceeds from the surface to the interior thereof, thereby resulting in the formation of wrinkled or roughened surface. This markedly reduces commercial value of cured products.
It is also proposed to use alkylene group-containing polyorganosiloxanes as additives for addition curable compositions (Japanese Patent Publication No. 3,774/79). Although the formation of wrinkled or roughened surface can be prevented in this case, the curing must be carried out under mild conditions at a temperature of around 100.degree. C., and hence an undesirably long period of time is required for the curing. In addition, the additive is inferior in its effect for preventing increase in viscosity during storage at room temperature.
It is proposed in U.S. Pat. No. 4,032,502 to use as an additive for addition curable compostions the following silane compounds: ##STR1## By the use of these stabilizers, there can be solved the problem of increase in viscosity during storage, as well as the problem of surface curing. However, long periods of time are required for the curing of compositions containing such stabilzers, in particular, when the compositions are cured under mild conditions. Therefore, the use of such stabilizers is disadvantageous in workability at the time of injection molding, or the like.
In Japanese Patent Publication No. 31,467/69 is disclosed for use in addition curable compositions a stabilizer a composition which is a product of alocoholysis of trimethoxysilane with an alcohol of the following formula: ##STR2## However, the product of the alcoholysis can be obtained only in the form of a mixture, and addition curable compositions obtainable by using a mixture as an additive suffer not only from viscosity increase during storage but also surface curing with hot air curing at elevated temperatures.
Accordingly, there can be obtained by the prior art no addition-curable polyorgasnosiloxanes which can be stored for long periods of time without increase in viscosity and which can be evenly cured in a short period of time under relatively mild conditions, without the formation of a wrinkled or roughened surface even when cured with hot air.
It is therefore an object of the present invention to provide a polyorganosiloxane composition which is free from the above disadvantages.